Recently, as wireless networks are spread, the lower cost and the lower power consumption of the networks have been desired. As a network formation realizing the lower cost and lower power, a multihop wireless network (hereinafter simply referred to as “multihop network”) has been known. The multihop network has a network formation that uses only wireless devices (hereinafter may be referred to as “wireless device”) having a wireless communication function to perform wireless communication by a multistage hookup and relay method and to provide an autonomous decentralized network.
One of multihop networks is a tree network. The tree network is formed by hierarchizing a plurality of wireless devices through multistage connection to establish a parent-child relationship among the devices.
FIG. 10 is a schematic view of a network system S100 forming a tree network by the first to eighth wireless devices D1 to D8. Here, data is transferred from the eighth wireless device D8 to the first wireless device D1 by the method as described below.
First, because the eighth wireless device D8 does not have a wireless device at a lower layer, the eight wireless device D8 transfers data to the fifth wireless device D5 at a higher layer. The fifth wireless device D5 confirms that the first wireless device D1 does not exist at the lower layer thereof and transfers the data to the second wireless device D2 at a higher layer. Similarly, the second wireless device D2 confirms that the first wireless device D1 does not exist at the lower layer thereof and transfers the data to the first wireless device D1 at a higher layer. The first wireless device D1 confirms that the transferred data is addressed to itself to perform a data reception processing.
As described above, the tree network having a hierarchical network can have an increased number of wireless devices by further hierarchization and is useful for the formation of a wide area network. According to an example of a known tree network, based on the time at which a parent node positioned above a node (wireless device) in the tree carries out the communication, a time slot for performing a carrier sense for data transmission by the node thereof is determined based on the value of ID of this node to avoid a communication collision (see Patent Publication 1).
Patent Publication 1: Japanese Patent Unexamined Publication No. 2005-94529